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Most women think that having herpes during pregnancy is a fairly straightforward matter: If you have any sores when you go into labor, you’ll simply deliver by Cesarean section to avoid infecting your baby. Yet the issue is much more complicated than is often perceived.

For example, herpes is far more prevalent than is generally recognized, and many people don’t know they’re infected or that they can contract the virus from a partner who has no symptoms. What’s more, few people realize that contracting herpes during pregnancy can be very dangerous to the baby. Here’s what every pregnant woman needs to know about this very common virus.

Your chances of having herpes may be greater than you think According to the Centers for Disease Control and Prevention, 16.2 percent of U.S. adults—1 in 6—have genital herpes caused by herpes simplex virus 2, or HSV-2. However, when you factor in the number of people who have genital herpes caused by HSV-1, the strain typically associated with fever blisters of the mouth, the number skyrockets to approximately 1 in 3, says David Kimberlin, M.D., a professor in the division of pediatric infectious diseases at the University of Alabama at Birmingham. “Yet 80 percent or more of them don’t know they have the virus, because they’ve never had noticeable symptoms,” he adds. According to a 2009 study in The New England Journal of Medicine (NEJM), an estimated 25 percent to 65 percent of pregnant women in the U.S. have HSV-1 or HSV-2 genital herpes. In other words, you could very well have the virus and not even know it ...

… and that may actually be a good thing If you contracted herpes before you got pregnant, your body has had time to develop antibodies to the virus, protection that you will pass on to your baby. According to Kimberlin, if you do have an established virus (as opposed to one acquired dur- ing pregnancy) and it is present in your genital tract during delivery, the risk of transmitting it to your baby is only about 2 percent.

Contracting herpes while pregnant poses serious risk to a baby If you get herpes for the first time during your pregnancy, particularly toward the end, and it is present in your genital tract when you deliver, the risk of transmitting it to your baby is between 25 percent and 60 percent, a 2003 study published in the Journal of the American Medical Association (JAMA) found.

Such an infection can cause problems not only with the baby’s eyes and skin, but with his brain and central nervous system as well. “HSV infections are life-threatening in neonates,” explains Anna Wald, M.D., M.P.H., medical director of the University of Washington Virology Research Clinic in Seattle and co- author of the NEJM study. “A significant percentage of babies who are infected die even if they receive anti-viral therapy, and a significant percentage of survivors are brain-damaged.”

Elizabeth Stein, C.N.M., M.S.N., M.P.H., a certified nurse-midwife in New York City who’s an expert in infectious diseases, explains that it takes the body between eight and 12 weeks to produce antibodies to the virus—which is why contracting herpes in late pregnancy is so dangerous. “Having a first infection toward the end of pregnancy is extremely dangerous,” she says. “Your body simply hasn’t had time to develop the antibodies necessary to prevent the virus from attacking the fetus.”

The real danger is if your partner has herpes and you don’t If your partner knows he has herpes, he will undoubtedly try to keep from spreading it to you by avoiding sexual contact if he has any lesions. The problem is that he can unwittingly infect you through a process called viral shedding; this occurs when the virus is active but doesn’t cause noticeable symptoms. This happens fairly often: A new study published in JAMA found that people infected with HSV-2 are shedding the virus 10 percent of the time. If your partner does have herpes and you don’t, Stein recommends the following:

»Don’t have sex This is especially important toward the third trimester.

»If you do have sex, use condoms However, according to the NEJM study, condoms are only about 50 percent effective at reducing the risk of HSV transmission. “A condom may not cover the area with the virus,” Stein explains.

»Don’t have oral sex Few people realize you can pass genital herpes to a partner’s mouth—and vice versa. “Both HSV-1 and HSV-2 are found in oral and genital locations,” Stein says. Wald adds that 50 percent of new genital herpes infections are caused by HSV-1; recurrences are usually HSV-2.

»Be ready to treat symptoms “Your partner needs to take the anti-viral medication Valtrex [valacyclovir] or Zovirax [acyclovir] if he suspects he’s having an outbreak,” Stein says. If you do have herpes, watch for symptoms If you think the virus is becoming active—tingling, pain or itching at the infection site are common symptoms—let your care provider know. She will likely want you to take an anti-viral medication; fortunately, these are safe during pregnancy. (Also let her know if you’ve been diagnosed with herpes, even if you haven’t had a recent outbreak.)

Many doctors and midwives put women with the virus—active or not— on one of these medications for the last four weeks of pregnancy, as studies have shown that doing so can reduce shedding and outbreaks; whether they actually protect the baby is unknown, however. If you do have an active infec- tion at delivery, your baby should be delivered by Cesarean section.

How do babies get herpes? “Eighty-five percent of neonatal infections occur when the baby passes through the birth canal, often when a woman is shedding the virus but has no symptoms,” says pediatric infectious disease specialist David Kimberlin, M.D. Ten percent of cases are contracted after delivery, often when someone with herpes fever blisters kisses the baby; the other 5 percent are contracted in utero. As for breastfeeding, if you have a herpes sore on your nipple or areola, don’t nurse on that side until it is completely healed. Cover the sore if you have one elsewhere on your breast.